Particulate filters have long been known and widely used. Particulate filters of various types have been utilized for decades in different applications, for example air filtration and analytical measurements in laboratories for a wide range of testing protocols.
Of recent importance is a method of gravimetric analysis. Gravimetric analysis is founded on the principle that a weight of a substance is the elementary measurement used for calculation. In the case of gravimetric analysis of particulate filter applications, the results of a weighing before (pre weighing) and after (post weighing) exposure to an air stream are compared to calculate the load of particulate within the volume of air to which the filter was exposed.
It is important in this calculation that the net load based upon the pre weighing and post weighing data is a result of the trapped particulate and not a variation of the mass of the filter itself. As smaller net loads have been of interest in industry, the requirements for precision and accuracy of the particulate filter gravimetric analysis have been becoming more stringent. Requirements to accurately weigh to the microgram (0.000001 g) level or sub-microgram level (0.0000001 g) are in place in the Code of Federal Regulations for both laboratories responsible for gravimetric fine particulate in the ambient air pollution market comprised of federal, state, county, and local environmental protection agencies, the Combustion Engine Manufacturers and their regulating laboratories, as well as laboratories performing chemical speciation via extraction techniques for the qualification and quantification of the particulate deposited on the filter.
For all interests involved, accurate and precise measurement of particulate filter net load is imperative. To date no known particulate filter has been designed to address specifically improved performance, stability, and usability at the microgram and sub microgram level and for various applications.